Overstroke control for free-piston units



Feb. 8, 1'949. D. E. MElTzLER 2,461,224

OVER'STROKE CONTROL FOR FREE-PISTON UNITS Filed Aug. 23, 1944 3 Sheets-Sheet l i n A o mi( a r m vo /g viinf- 2 0 @"G' 0 O) O) D (D J N 0 O C (D O \...N

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INVENTOR L"Fel-L 8, 1949. I .v E. MEITZLER 2,461,224

OVERSTROKE CONTROL FOR FREE-PISTON UNITS `Filed Aug. 25. 1944 A 3 Sheets--Shee'cl 3 Patented Feb. 8, 19449l t.

Donald E. Meitzler, Manchester, iflonn.,

to United Aircraft Corporation,

assigner East Hartford,

Conn., a corporation of Delaware 'Application August 23, 1944, serial No. 550,896

' 1 claim. (ci. 23o- 56) This invention relates to a control for. the fuel supply to a free-piston unit. The length and position of the piston stroke in a free-piston unit are affected by changes'in the operating conditions, and unless such changes are compensated for, the length of the stroke may, under certain conditions, become excessive. A feature of this invention is a control for the fuel supply which becomes operative in the event of piston overstroke.

Another feature is a fuel cut-oif which shuts off the fuel supply and stops the unit when the end position of the piston stroke is outside the desired limits.

The copending application of Kalltinsky, Serial No. 550,883, filed August 23, 1944, on which Patent 2,420,483 has been issued, discloses a stroke indicating device or master control for the plstons of a free-piston unit. A featureof the present invention is the control of the fuel supply in response to an indicating device of this character.

Other objects and advantages will be apparent from the speciiication and claim, and from the accompanying drawings which illustrate an em` oodiment of the invention.

Fig. l is a sectional view through the unit.

Fig. 2 is a sectional view showing the restraining linkage for the pistons.

Fig. 3 is a diagrammatic view of the master control and the control for the fuel supply.

The unit shown includes an engine cylinder -l having reciprocating pistons |2 and I4 to which compressor pistons I6 and I8 in cylinders and 22 are integrally connected. Sleeves 24 and 26 attached to the compressor pistons complete the reciprocating piston assemblies. The sleeves in combination with stationary pistons 28 and 30 form air spring cylinders.

The piston assemblies are moved apart by the burning of fuel injected into engine cylinder 0 through one or more nozzles 32. Air compressed in the air spring cylinders on the power stroke returns the piston assemblies. The assemblies are always maintained at' equal distances from the center of the'engine cylinder by a linkage, which may include racks 34 .and 36, Fig. 2, extending from the piston assemblies and meshing with a pinion `:i8 on a shaft 40.

Intake manifold 42, which extends around the compressor and `engine cylinders, conducts air to intake valves 44 in the heads of the compressor cylinders through which air alternately enters opposite ends of .these cylinders. The compressed air leaves the cylinders through discharge valves 46, also at opposite ends of the compressor cylinders and passes into a central scavenge-chamber 48 and end chambers 50 and 52. These chambers may be connected by a scavenge manifold, not shown.

Compressed gas from the chambers enters engine ports 54 and 56 which are uncovered by pistons l2 and |'4 at the end of the power stroke, thereby permitting air to be blown through the engine cylinder. Gas in the engine cylinder is discharged through exhaust ports 58 into ex haust manifold 60.

The location of the outer end of the piston stroke is indicated by a master control 62. This control is actuated by a cam 64 turning with the pinion 38, as shown in Fig. 2. Since this pinion is oscillated directly from the pistons, the movement of cam 64 proportional to the piston stroke.

Fluid under pressure from a constant pressure source enters a passage l0 in a casing 'l2 through a conduit 14. This passage intersects a bore 16 adjacent its outer end and a throttling screw 'I8 controls the rate of flow into bore 16. A branch passage 80 from passage 10 connects with a, port 82 in bore 'I6'. A plunger 84 in bore 16 has a groove 86 which connects a port 88 alter- Y nately with port 82 or a port 90. Port 88 is connected by a passage 92 to the inner end of bore 16. Port is connected by a channel 94 in casing 'l2 and in an adjacent casing 96 to the inner end of a bore -98 in casing 96.

A piston |00 in bore 98 is moved to the right by a calibrated spring |02. A plunger |04 extends through the piston and carries on its projecting end a push rod |08. This rod' has a roller 0 held against cam 64 by a spring I I2. Plunger |04 has a central passage ||4 connected with spaced grooves I6 and H8 in the plunger. Groove ||6 aligns with openings|20 in a sleeve |22 carried by piston |00-and groove ||8 is adapted to be uncovered by the end of sleeve |22 as the plunger is moved to the right by the cam as the pistons approach the outer ends of their stroke.

Fluid under pressure from the right hand end of bore 1B enters the outer end of bore 98 thrdughV a connecting channel |24, moving piston |00 against the action of spring' |02. As plunger |04 is moved by cam 64 the groove ||8 is uncovered by sleeve |22 to permit discharge of fluid from the right hand end of bore 98. The pressure in the right hand end of bore 98 variesy in accordance with the compression of the springand as the piston. stroke becomes'shorter, the piston |00 3 r moves inward increasing the spring tensionand increasing the pressure at the end of bore 88.

` and the pressure at opposite ends ot the Since the change in pressure on the outer end of plunger 84 is proportional to the change in the location of the end position of the piston pressure (and change in pressure) may indicate on a calibrated gauge (not shown) the exirct position of the end of the piston stroke and may be used for actuating the fuel control means.

The outer end of plunger |04 may reciprocate in a chamber |30 connected byla conduit |32 to a sump, not shown. The inner end of bore 98 may be connected by a conduit |34 to conduit |32. It may be advantageous to reducel pressure surges in channel 4 by means of a bellows |38.

Control fluid from the outer master control may be used to cut oi! the supply of fuel in the event that the length of stroke becomes excessive or if the end of the 'actual piston stroke approaches outer dead center. As shown conduit I26'is connected to a port |42 in acasing |44 for the overstroke control. This port communicates with the end of a bore |48 in which a plunger |48 is slidable, this plunger being held in the position shown by a spring |50.

Plunger |48 has a projecting stem |52 on the end of which is a tapered plug |54 engaging a seat |56 between therfuel inlet port |58 and the fuel outlet port |80 ,which is connected to the injection system |62. The injection system may be of the type shown in the coopending application of Meitzler, Serial Number486,625, led May 11, 1943.

\Duri ng the normal lstrike of the free-piston compressor the control iiuid from thel master control has `a high enough pressure to move plunger |48 downwardly against the action of spring |50 to move the plug- |54 away from its seat and permit fuel to reach the injection system. As the length of the stroke becomes excessive thereby causing the actual outer end position of the piston stroke to approach outer dead center the pressure of the control uidu decreases, permitting valve plug |54 to be moved upwardly for reducing the fuel supply to the engine. The tendency oi.' a reduction in the fuel supply is to shorten the piston stroke. It the outer end of the actual piston stroke continues to approach the outer dead center position the valve will be closed more and more until plug |54 seats fully 'and cuts of: the supply of fuel to the injection system.

In operation, the., piston assemblies normally reciprocate in such a way that the engine pistons-` do not touch on the inward stroke and the com- 'pressor pistons do not go far enough on the outplunger 84. It the engine piston stroke shortens, the pressure builds up on the piston |00 moving it to the left until it reaches a position such that the groove I |8 will be uncovered at the outer end of the engine piston stroke. This increase in pressure, as the stroke shortens, is transmitted to the gage |28 and also to the bore |48 thereby moving the valve |54 down to increase the flow area for the fuel through the valve |44 to the fuel injection system. I

Conversely, if the stroke of the engine' piston increases in length, thelplunger |04 is moved iari' ther to the right at the outer end of each piston stroke thereby venting the space at" the right of the piston |00 to allow the piston |00 to move toward the right thereby reducing the pressure at opposite ends of the plunger 84. This reduced pressure is transmitted through conduit |28 to bore |48 thereby allowing the valve plug |54 to the flow area through the over-stroke control. If the length of the piston stroke becomes excessive,`the pressure in the bore |48 will drop to such an extent that the supply o1 fuel to the injection system will be completely out off to stop the freepiston unit.

It is to be understood that the invention is not limited to the specific embodiment herein illustrated and\described but may be used in other ways without departure from its spirit as defined .by the following claim.

I claim: v A free-piston unit including an engine cylinder and piston, means for injecting fuel into said engine cylinder, means responsive to piston movement for changing the pressure of a control fiuid proportionally to the change in the position of the piston at the end of successive strokes, and a plunger actuated by said control fluid and movable in response to changes in pressure of said fluid, `a valve mechanically connected to and movable at all times with said plunger, said valve being controlled by saidplunger for cutting on the supply of fuel to "said injecting means if the piston moves beyond a predetermined limit and a spring acting on said valve and plunger.l in a direction to open ,saidvalve in opposition to the pressure of said control fluid on said plunger.

DONALDE. MEITZLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,038,442 Pescara Apr. 21, 1936 2,064,976 Janicke Dec. 22, 1936 2,084,823 Pateras-Pescara June 22, 1937 2,086,228 Janicke July 6, 1937 2,090,709 Steiner Aug. 24, 1937 2,102,121 Janicke Dec. 14, 1937 2,147,935 Steiner Feb. 21, 1939 2,168,828 Pescara ...l,.-.. Aug. 8, 1939 2,182,063 Steiner Dec. 5, 1939 2,200,892 Pateras-Pescara May 14, 1940 2,344,058 Pateras-Pescara Mar. 14, 1944 2,434,778 Welsh Jan. 20, 1948 Y 2,434,877 Welsh et al. Jan. 20, 1948 FOREIGN PATENTS Number l Country Date 438,929 Great Britain Nov. 26, 1935 541,779 Great Britain Dec. 11, 1941 

